A problem in the field of vertebral implants and notably of corpectomy cages sometimes relates to the deployment of an implant capable of replacing a vertebral segment, sometimes with a large size, at least in height, for a corpectomy cage since the vertebral segment may correspond to all or part of at least one vertebral body and/or at least one intervertebral disc. Indeed, certain pathologies, notably cancer diseases, may result in a degradation of the vertebral bodies (either partly or completely) and/or of the intervertebral discs. It is then sometimes desirable to replace the lesioned vertebral segments(s) with an implant of significant height. Further, it is often desirable to be able to modulate the height of the implant during surgery since the ablation of the lesioned structures generally require distraction of the vertebrae for restoring a physiological (or less pathological) height to the treated vertebral segment and this height varies according to the extent of the lesions (for inserting the implant between healthy tissues).
A problem related to the height of the implants sometimes involves the stabilization of the implant against the vertebral structures between which it is inserted. The required distraction is sometimes not very compatible with numerous stabilization solutions, such as notches on the contact surfaces of the implants, since these notches often make it necessary to make an additional distraction for inserting the implant. Further, the anchoring of the implant is generally preferable to simple notches which generally only limit the risk of movement but do not enhance reliable immobilization.
In the prior art, solutions are known, notably for corpectomy, such as expandable cages in situ, generally comprising a body including moveable elements providing the vertebral contact surfaces and giving the possibility of increasing the height of the implant once the latter is inserted between the vertebrae. These solutions have the drawbacks of relying on generally complex and costly mechanisms, which often make the implant and/or the vertebrae fragile since the distraction obtained by the implant during its expansion often does not give the possibility of estimating the exerted force because the surgeon often does not feel enough the force he/she generates during the distraction (such that the implants sometimes collapse in the vertebrae). Further, they often provide a reduced grafting space, not allowing the addition of a bone graft or substitute, sufficient for quality arthrodesis. Similarly, such implants are often made of metallic material, which does not allow viewing of the bone growth into the cage during inspections by post-operative imaging. On the other hand, these solutions often have a small expansion ratio (1/3) and therefore generally require that the compressed implant already have a significant size so that its size is satisfactory when it is expanded and the design of these cages makes it often necessary to release the distraction in order to allow insertion into the vertebral segment. Moreover, as the vertebrae can be deformed or crushed or even packed, the implant must be able to be inserted with the smallest possible height and then to be enlarged to the maximum. These types of expandable cages are often incompatible with notches or teeth for stabilization (since the latter reduce the actual distraction capability, interfere with the positioning and risk making the adjacent vertebral structures fragile) and/or with anchoring (since the cages generally do not provide a sufficiently wide structure for retaining an anchoring means). Moreover, anchoring with screws may prove to be tedious to set into place and requires an overly invasive approach.
Other problems, often related to expandable cages in situ and to the drawbacks of certain of the solutions of the prior art, sometimes relate to the insertion of the implant into the rachis, which is generally difficult on the one hand and the assembling and locking of the various elements of the implant, which have to be sufficiently easy and reliable for providing a solution limiting the dislocation risks of the implant on the other hand.
Another problem in the field relates to invasivity and in particular to accessing the intervertebral spaces (discal spaces) which is often particularly delicate because of the congestion, notably because of the presence of blood vessels and nerves in the neighborhood of the intervertebral space, as well as the proximity of the spinal cord. The bone anchoring devices which have to penetrate sufficiently deeply into the vertebrae for ensuring proper attachment, therefore also have to have a small enough size and allow attachment of the implant without jeopardizing the surrounding blood vessels and nerve tissues (for example not requiring more space in the surroundings of the intervertebral space than necessary for implanting the actual rachidian implant). Such anchoring means therefore preferably also have to address the problem of limiting invasivity, in addition to reliability and stability.
Another problem for bone anchoring means often related to the drawbacks of certain of the solutions of the prior art, sometimes relates to the removal of the bone anchoring means and/or of the implant, since removal is generally impossible or difficult. Indeed, it is generally desired to be able to remove the bone anchoring means (and generally the implant). Therefore the bone anchoring means preferably can be retained in the implant in a stable way but they may also be removed as easily as possible. Further, easy removal should also be preferably achieved with an invasivity as limited as possible.
In this context, it is worth proposing various embodiments of implants that address one or more of the known problems, for example by being easily implantable, robust and reliable, and adaptable in different sizes and preferably expandable within the patient, perhaps notably by limiting the dislocation risks and/or which may limit the risks of making the adjacent vertebral structures fragile and/or which allow anchoring in the vertebral bodies without compromising the final positioning, for example while allowing removal and/or avoiding greater distraction than required for inserting the implant.